At the London docks, armed men stand guard over a Russian ship. Seaman Stephen Vasa tries to sneak past them and make his way to shore, but is spotted. He tries to get to a waiting car and the female driver, Stephen’s wife Sonia, but the sailors catch up to him and overwhelm him, while the ship’s captain grabs the woman and says that they knew her husband would try to get to her and the whole thing was a trap.
At the Castle Hill Laboratories, Mr. Bratski with a refugee protection organization meets with Peter. He asks for his help rescuing Stephen but Peter says that he can’t become involved in every problem that comes along. Bratski explains that Stephen is a national and that the police can do nothing, and that he failed to escape before in New York City. The refugee organization would like Peter to become involved illegally, but Peter notes that he could spend his whole life freeing refugees and still never succeed. The scientist claims that science has more to offer than one man’s freedom, and Bratski is disgusted. He walks out as Diane comes in, and she asks Peter who he is abandoning. Peter briefly explains and then calls Sir Charles and has him check on Bratski. Sir Charles confirms that Bratski is valid and suggests that Peter might help him. When he learns that Bratski wants Peter to do something illegal, Sir Charles says that the less he knows the better.
Peter decides to look into the matter, removes his clothing, and has Diane drive him to the docks. As they leave, two men follow them. At the docks, Diane poses as a reporter and asks about the seaman who tried to escape. The local officer and a worker don’t know anything other than that Sonia was parked nearby. As they drive to Sonia’s hotel, Diane spots the men following them and Peter points out that he spotted them ever since they left Castle Hills. Diane lets Peter out and then drives randomly to draw away their pursuers.
Peter checks the register at the hotel and then takes the elevator to Sonia’s room. An elderly woman gets in the elevator, carrying her dog, and is surprised when she discovers no one is there. Peter gets out on his floor and goes to Sonia’s room. She’s meeting with Bratski and is worried that there is no hope for her husband. Peter comes in and tells them that he’ll help rescue Stephen, and leaves with Bratski. Once they’re gone, Sonia calls to tell the commissar aboard the ship that Peter is on his way. The commissar assures her that once he has Peter captured, he’ll release Stephen. Once he hangs up, the commissar tells the captain to capture Peter alive, and the captain shows him the radar unit that they have developed that will let them locate Peter despite his invisibility.
Bratski drives Peter to the dock and the invisible man goes through the gate. The radar unit picks him up and the captain tells his men to gather on the gangplank, the only way aboard. When Peter comes up it, the sailors drop a net on him and tie him up before he can call for help, and then drop him into the hold. Sonia arrives and demands to talk to the captain as the ship leaves. She presents her papers and the police officer at the gate lets her through. The commissar hears her and decides to let her on board rather than let Sonia make a scene. They bring her up while the officer at the gate recognizes her as Stephen’s wife and sends his partner to make a call. The commissar takes Sonia to the battered Stephen and tells them that they will be taking Sonia with them.
The sailors try to secure Peter but he gets free and ducks into the hold. They seal off the door and Peter starts throwing bags at them. As the ship leaves the dock, Peter gets out the door and locks it behind him.
The official at the Port Authority receives word that Sonia went aboard the ship and never came off. The port official decides to make some inquiries and calls the ship. The captain says that Sonia has decided to go home with her husband, and the official asks to speak with Sonia. The commissar has no choice but to put her on the lines but promises to make Stephen suffer if she doesn’t cooperate. The official has her provide sufficient identification and then asks if she is traveling of her own free will. Sonia says that is and the official wishes her well, and the commissar escorts her back to Stephen’s cabin.
Peter gets to Stephen’s cabin first and tells him to be ready for a rescue. When a sailor arrives with Sonia, Peter knocks the man out but Stephen warns that they’re too far out for Sonia to swim. Peter goes to the wheelhouse and sends mixed signals to the engine room. The engineer calls to demand answers and the captain tells him to maintain speed. Peter attacks the captain and swings the ship around so that it smashes into the pier. When they hit, Stephen and Sonia jump over the side and make their escape.
Later, Peter meets the happy couple at Sonia’s hotel room and confirms that thanks to Sir Charles, Stephen has permission to stay. Sonia apologizes but Peter understands that she didn’t have a choice and wishes them well. He takes the elevator down again, and makes conversation with the same confused woman with a dog from before.